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Fix race in SSI interaction with gin fast path. 

The ginfast.c code previously checked for conflicts in before locking
the relevant buffer, leaving a window where a RW conflict could be
missed.  Re-order.

There was also a place where buffer ID and block number were confused
while trying to predicate-lock a page, noted by visual inspection.

Back-patch to all supported releases.  Fixes one more problem discovered
with the reproducer from bug #17949, in this case when Dmitry tried
other index types.

Reported-by: Artem Anisimov <artem.anisimov.255@gmail.com>
Reported-by: Dmitry Dolgov <9erthalion6@gmail.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/17949-a0f17035294a55e2%40postgresql.org
This commit is contained in:
Thomas Munro 2023-07-03 16:20:01 +12:00
parent 814f3c8e48
commit 13f127800f
2 changed files with 10 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
src/backend/access/gin/ginfast.c
View File

@ -244,9 +244,10 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
/*
* An insertion to the pending list could logically belong anywhere in the
* tree, so it conflicts with all serializable scans. All scans acquire a
* predicate lock on the metabuffer to represent that.
* predicate lock on the metabuffer to represent that. Therefore we'll
* check for conflicts in, but not until we have the page locked and are
* ready to modify the page.
*/
CheckForSerializableConflictIn(index, NULL, metabuffer);
if (collector->sumsize + collector->ntuples * sizeof(ItemIdData) > GinListPageSize)
{
@ -290,6 +291,8 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
LockBuffer(metabuffer, GIN_EXCLUSIVE);
metadata = GinPageGetMeta(metapage);
CheckForSerializableConflictIn(index, NULL, metabuffer);
if (metadata->head == InvalidBlockNumber)
{
/*
@ -352,6 +355,8 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
char *ptr;
char *collectordata;
CheckForSerializableConflictIn(index, NULL, metabuffer);
buffer = ReadBuffer(index, metadata->tail);
LockBuffer(buffer, GIN_EXCLUSIVE);
page = BufferGetPage(buffer);

4
src/backend/access/gin/ginget.c
View File

@ -139,7 +139,9 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
* Predicate lock entry leaf page, following pages will be locked by
* moveRightIfItNeeded()
*/
PredicateLockPage(btree->index, stack->buffer, snapshot);
PredicateLockPage(btree->index,
BufferGetBlockNumber(stack->buffer),
snapshot);
for (;;)
{